Stromatolites rank among the most productive ecosystems on Earth, with extremely high rates of element cycling, especially carbon, oxygen, nitrogen, iron, and sulfur. Their study provides critical insights into early microbial life evolution, environmental conditions, and associated biogeochemical cycling. Specifically, carbon, nitrogen, and sulfur isotopes can be used to assess metabolic activities of microbial communities, including those that may regulate the formation and preservation of modern and ancient stromatolites, such as photosynthesis, nitrogen fixation, and sulfate reduction. Moreover, while Precambrian stromatolites’ isotopic signals can record microbial communities that both influence and adapt to changing major redox conditions such as the Great Oxidation Event, local and secondary processes can open a window onto microbial evolution such as the early evolution of bacterial sulfate reduction.
Stromatolites are widespread in Precambrian sedimentary successions and provide important insights into life, environmental processes, and surface conditions on the young Earth. Shaped by interactions among microbial processes, sediment deposition, and mineral precipitation, stromatolites have a record spanning most of Earth’s history and are sensitive indicators for past hydrodynamic conditions and water chemistry. Significant variations in the composition, texture, and structure of stromatolites and associated sedimentary facies occur throughout the geological record, constraining the evolution of surface conditions. The ability of microbial communities to build large carbonate platforms in turn actively influenced the Precambrian hydrosphere and atmosphere. Stromatolites are direct, visible evidence of microbial ecological success that shaped the Precambrian Earth’s surface.
Stromatolites represent some of the oldest and most persistent records of life on Earth. These organo-sedimentary structures have formed through complex interactions between microorganisms and their environment for nearly 3.5 billion years. Here, we trace the evolving scientific narrative surrounding these structures, from their early 19th-century descriptions to their integration into the broader concept of microbialites. This journey reflects a profound conceptual shift: once classified as distinct fossil species, stromatolites are now understood as mineralising ecosystems and dynamic biogeochemical archives. This modern perspective allows for the reconstruction of early life and its environment while highlighting key scientific challenges, such as disentangling microbial from environmental controls and interpreting biogenicity in ancient terrestrial and extra-terrestrial rocks.
Quartz is a key archive of Earth surface processes, recording erosion, burial, transport, and landscape evolution across a wide range of timescales. Recent advances in quartz-based analytical techniques have expanded the potential for integrative geochemical and geochronological approaches. Fourier-transform infrared spectroscopy (FTIR) enables detailed characterization of quartz provenance and geological history, while terrestrial cosmogenic nuclides (TCNs) constrain surface exposure, burial histories, and denudation rates. Optically stimulated luminescence (OSL) provides robust age control for fine-grained sediment transport and deposition, and ongoing developments in electron spin resonance (ESR) extend chronological constraints into previously inaccessible time ranges. Understanding the principles and limitations of each method is essential for their effective individual and combined applications in reconstructing Earth surface processes.
Quartz and other silica minerals are amongst the most important constituents of the Earth’s crust, both as rock-forming mineral components and as tools for understanding Earth processes. Quartz and other forms of silica are essential parts of both the geological and biochemical cycles with the potential to help us understand the processes of our planet across disciplines. This article is a narrative of quartz, starting with its crystallization from fractionated, silica-rich magmas, transport, and deposition of silica by hydrothermal fluids, as well as physical, chemical, and biogenic processes resulting in silica weathering, transport, accumulation, and the formation of sedimentary silica deposits. Extraterrestrial quartz and silica occurrences are also discussed.
The use of microcrystalline silica has been documented among early hominins, with significant diversification over the last ~3 million years, from early toolmaking to applications in personal adornment and symbolic contexts. From the Oldowan onwards, both microcrystalline quartz and amorphous silica are consistently observed in the archaeological record, and they shaped aspects of human technological and behavioral evolution. This article offers insights into how mechanical, environmental, and cultural factors guided the selection of silica materials and their transformation to purposeful objects—from Pliocene hominins through to the Middle Ages. The crystal chemistry that imbues microcrystalline quartz varieties with their unique properties is reviewed, and the formation pathways for biogenic and abiogenic microcrystalline and amorphous silica are considered.
Humankind’s use of silica raw materials began at least 1.85 million years ago with production of flint tools and spans to today’s more than 1000 industrial applications, all relying on its chemistry and specific physical properties. Among the key achievements are the discovery of the piezoelectric effect of quartz for timekeeping, the critical importance of silicon-based semiconductor technologies for the digitalization of our society, and the production of renewable energy through photovoltaics. One of the greatest challenges regarding raw material supply and security lies in identifying new quartz deposits of sufficient purity, size, and properties to meet increasing demands. Although quartz is mined from a variety of deposits, economically viable sources remain difficult to locate for reasons that we explain.
Quartz is the most popular and widely used gemstone of the SiO2 family with its phenomenal varieties and spectacular colors, e.g., near-colorless (rock crystal), purple (amethyst), yellow (citrine), smoky (smoky quartz), and pink. The colors of these varieties are mostly caused by trace contents of foreign ions, which in turn are activated by treatment with high-energy radiation and/or temperature treatment (so-called color centers). Cryptocrystalline SiO2 varieties such as agate, chrysoprase, or jasper mostly represent mixtures of SiO2 minerals and other phases, while the play of colors in amorphous precious opal is caused by light diffraction and interference. Despite their different origins and properties, all these SiO2 varieties have played a dominant role as gemstones and cut stone since antiquity.
Despite their simple chemical composition, silica (silicon dioxide, SiO2) minerals comprise a complex system with diverse polymorphs of distinct crystal structures and different stabilities and properties. Quartz is arguably the most important mineral throughout human history, from early survival tools to critical materials for modern advanced technology. In addition, quartz and other silica polymorphs and varieties are excellent archivers and important tools for deciphering geological, environmental, and planetary processes and histories.
Minerals, especially crystalline ones, are generally anisotropic, meaning that some of their properties depend on direction. A spectacular example is cordierite, which, depending on the direction in which it is viewed in transmission, will appear purple or yellow.
